Efficient,Polarization-Diverse State Generation withTunable Black Phosphorus Cavity Heterostructures and Active Metasurfaces

The dynamic, on-demand generation of different polarization states of light has diverse applications in optical communications, imaging, sensing, and quantum information processing. Such active polarization control is typically achieved using active metasurfaces or spatial light modulators based on liquid crystal media that have limited switching speeds and conversion efficiency. Layered van der Waals low-dimensional materials provide new avenues for more versatile polarization control with an operating frequency several orders of magnitude higher than that for liquid crystal devices. Here, we report the design of a heterostructure for efficient, polarization-selective free-space phase modulation or amplitude modulation by integrating electrically tunable, optically anisotropic black phosphorus (BP) into high quality factor (Q ∼ 7500 to 11000) distributed Bragg reflector-based Fabry–Perot cavities. These devices achieve a respective phase tuning range of 210° and an amplitude tuning range of 99%. We also introduce designs for BP heterostructures that employ two twisted cross-aligned BP layers that are able to access polarization states covering 75% of the Poincaré sphere from voltage tuning alone. Finally, we introduce a design for an active metasurface polarization beam splitter based on our cavity heterostructures with an electrically tunable angle of diffraction that leverages spatially engineered polarization gradients. These structures open a pathway for further structuring of light by controlling the phase and amplitude along independent orthogonal directions.